1.1. Field of the Invention
The present invention provides new proteins for combating insects, and particularly, coleopteran, dipteran, and lepidopteran insects sensitive to the disclosed δ-endotoxins derived from Bacillus thuringiensis. The invention provides novel chimeric crystal proteins and the chimeric cry gene segments which encode them, as well as methods for making and using these DNA segments, methods of producing the encoded proteins, methods for making synthetically-modified chimeric crystal proteins, and methods of making and using the synthetic crystal proteins.
1.2. Description of Related Art
1.2.1 B. thuringiensis Crystal Proteins
The Gram-positive soil bacterium B. thuringiensis is well known for its production of proteinaceous parasporal crystals, or δ-endotoxins, that are toxic to a variety of lepidopteran, coleopteran, and dipteran larvae. B. thuringiensis produces crystal proteins during sporulation which are specifically toxic to certain species of insects. Many different strains of B. thuringiensis have been shown to produce insecticidal crystal proteins, and compositions comprising B. thuringiensis strains which produce proteins having insecticidal activity have been used commercially as environmentally-acceptable insecticides because of their toxicity to the specific target insect, and non-toxicity to plants and other non-targeted organisms.
Commercial formulations of naturally occurring B. thuringiensis isolates have long been used for the biological control of agricultural insect pests. In commercial production, the spores and crystals obtained from the fermentation process are concentrated and formulated for foliar application according to conventional agricultural practices.
1.2.2 Nomenclature of Crystal Proteins
A review by Höfte et al., (1989) describes the general state of the art with respect to the majority of insecticidal B. thuringiensis strains that have been identified which are active against insects of the Order Lepidoptera, i.e., caterpillar insects. This treatise also describes B. thuringiensis strains having insecticidal activity against insects of the Orders Diptera (i.e. flies and mosquitoes) and Coleoptera (i.e. beetles). A number of genes encoding crystal proteins have been cloned from several strains of B. thuringiensis. Höfte et al. (1989) discusses the genes and proteins that were identified in B. thuringiensis prior to 1990, and sets forth the nomenclature and classification scheme which has traditionally been applied to B. thuringiensis genes and proteins. cry1 genes encode lepidopteran-toxic Cry1 proteins. cry2 genes encode Cry2 proteins that are toxic to both lepidopterans and dipterans. cry3 genes encode coleopteran-toxic Cry3 proteins, while cry4 genes encode dipteran-toxic Cry4 proteins, etc.
Recently a new nomenclature has been proposed which systematically classifies the Cry proteins based upon amino acid sequence homology rather than upon insect target specificity. This classification scheme is summarized and regularly updated in a database maintained by the Bacillus thuringiensis Delta-Endotoxin Nomenclature Committee at the following web site address: